simulated environment challenges to find optimal configurations giving the best
results with a lowest residual error and in the best of execution time.
-<<<<<<< HEAD
-To our knowledge, there is no existing work on the large-scale simulation of a
-real AIAC application. The aim of this paper is twofold. First we give a first
-approach of the simulation of AIAC algorithms using a simulation tool (i.e. the
-SimGrid toolkit~\cite{SimGrid}). Second, we confirm the effectiveness of
-asynchronous mode algorithms by comparing their performance with the synchronous
-mode. More precisely, we had implemented a program for solving large
-linear system of equations by numerical method GMRES (Generalized
-Minimal Residual) \cite{ref1}. We show, that with minor modifications of the
-initial MPI code, the SimGrid toolkit allows us to perform a test campaign of a
-real AIAC application on different computing architectures. The simulated
-results we obtained are in line with real results exposed in ??\AG[]{ref?}.
-SimGrid had allowed us to launch the application from a modest computing
-infrastructure by simulating different distributed architectures composed by
-clusters nodes interconnected by variable speed networks. In the simulated environment, after setting appropriate
-network and cluster parameters like the network bandwidth, latency or the processors power,
-the experimental results have demonstrated a asynchronous execution time saving up to \np[\%]{40} in
-compared to the synchronous mode.
-\AG{Il faudrait revoir la phrase précédente (couper en deux?). Là, on peut
- avoir l'impression que le gain de \np[\%]{40} est entre une exécution réelle
- et une exécution simulée!}
-\CER{La phrase a été modifiée}
-
-This article is structured as follows: after this introduction, the next section will give a brief description of
-iterative asynchronous model. Then, the simulation framework SimGrid is presented with the settings to create various
-distributed architectures. The algorithm of the multisplitting method based on GMRES \LZK{??? GMRES n'utilise pas la méthode de multisplitting! Sinon ne doit on pas expliquer le choix d'une méthode de multisplitting?} \CER{La phrase a été corrigée} written with MPI primitives and
-its adaptation to SimGrid with SMPI (Simulated MPI) is detailed in the next section. At last, the experiments results
-carried out will be presented before some concluding remarks and future works.
-=======
+
To our knowledge, there is no existing work on the large-scale simulation of a
real AIAC application. {\bf The contribution of the present paper can be
summarised in two main points}. First we give a first approach of the
written with MPI primitives and its adaptation to SimGrid with SMPI (Simulated
MPI) is detailed in the next section. At last, the simulation results carried
out will be presented before some concluding remarks and future works.
->>>>>>> 6785b9ef58de0db67c33ca901c7813f3dfdc76e0
+
\section{Motivations and scientific context}
\CER{On voulait en fait montrer la simplicité de l'adaptation de l'algo a SimGrid. Les problèmes rencontrés décrits dans ce paragraphe concerne surtout le mode async}\LZK{OK. J'aurais préféré avoir un peu plus de détails sur l'adaptation de la version async}
\CER{Le problème majeur sur l'adaptation MPI vers SMPI pour la partie asynchrone de l'algorithme a été le plantage en SMPI de Waitall après un Isend et Irecv. J'avais proposé un workaround en utilisant un MPI\_wait séparé pour chaque échange a la place d'un waitall unique pour TOUTES les échanges, une instruction qui semble bien fonctionner en MPI. Ce workaround aussi fonctionne bien. Mais après, tu as modifié le programme avec l'ajout d'un MPI\_Test, au niveau de la routine de détection de la convergence et du coup, l'échange global avec waitall a aussi fonctionné.}
Note here that the use of SMPI functions optimizer for memory footprint and CPU usage is not recommended knowing that one wants to get real results by simulation.
-As mentioned, upon this adaptation, the algorithm is executed as in the real life in the simulated environment after the following minor changes. First, all declared
-global variables have been moved to local variables for each subroutine. In fact, global variables generate side effects arising from the concurrent access of
-shared memory used by threads simulating each computing unit in the SimGrid architecture. Second, the alignment of certain types of variables such as ``long int'' had
-also to be reviewed.
+As mentioned, upon this adaptation, the algorithm is executed as in the real life in the simulated environment after the following minor changes. First, the scope of all declared
+global variables have been moved to local to subroutine. Indeed, global variables generate side effects arising from the concurrent access of
+shared memory used by threads simulating each computing unit in the SimGrid architecture.
+%Second, the alignment of certain types of variables such as ``long int'' had also to be reviewed.
\AG{À propos de ces problèmes d'alignement, en dire plus si ça a un intérêt, ou l'enlever.}
-\CER{Ce problème fait partie des modifications que j'ai dû faire dans l'adaptation du programme MPI vers SMPI. IL découle de la différence de la taille des mots en mémoire : en 32 bits, pour les variables declarees en long int, on garde dans les instructions de sortie (printf, sprintf, ...) le format \%lu sinon en 64 bits, on le substitue par \%llu.}
- Finally, some compilation errors on MPI\_Waitall and MPI\_Finalize primitives have been fixed with the latest version of SimGrid.
+\CER{Ce problème fait partie des modifications que j'ai dû faire dans l'adaptation du programme MPI vers SMPI. IL découle de la différence de la taille des mots en mémoire : en 32 bits, pour les variables declarees en long int, on garde dans les instructions de sortie (printf, sprintf, ...) le format \%lu sinon en 64 bits, on le substitue par \%llu. La phrase a été enlevé.}
+Second, some compilation errors on MPI\_Waitall and MPI\_Finalize primitives have been fixed with the latest version of SimGrid.
In total, the initial MPI program running on the simulation environment SMPI gave after a very simple adaptation the same results as those obtained in a real
environment. We have successfully executed the code in synchronous mode using parallel GMRES algorithm compared with our multisplitting algorithm in asynchronous mode after few modifications.
\caption{2 clusters, each with 50 nodes}
\label{tab.cluster.2x50}
- \begin{mytable}{6}
+ \begin{mytable}{5}
\hline
- bandwidth (Mbits/s)
- & 5 & 5 & 5 & 5 & 5 & 50 \\
+ bandwidth (Mbit/s)
+ & 5 & 5 & 5 & 5 & 5 \\
\hline
latency (ms)
- & 0.02 & 0.02 & 0.02 & 0.02 & 0.02 & 0.02 \\
+ & 0.02 & 0.02 & 0.02 & 0.02 & 0.02 \\
\hline
power (GFlops)
- & 1 & 1 & 1 & 1.5 & 1.5 & 1.5 \\
+ & 1 & 1 & 1 & 1.5 & 1.5 \\
\hline
size
- & 62 & 62 & 62 & 100 & 100 & 110 \\
+ & 62 & 62 & 62 & 100 & 100 \\
\hline
Precision
- & \np{E-5} & \np{E-8} & \np{E-9} & \np{E-11} & \np{E-11} & \np{E-11} \\
+ & \np{E-5} & \np{E-8} & \np{E-9} & \np{E-11} & \np{E-11} \\
\hline
\hline
Relative gain
- & 2.52 & 2.55 & 2.52 & 2.57 & 2.54 & 2.53 \\
+ & 2.52 & 2.55 & 2.52 & 2.57 & 2.54 \\
\hline
\end{mytable}
\bigskip
- \begin{mytable}{6}
+ \begin{mytable}{5}
\hline
- bandwidth (Mbits/s)
- & 50 & 50 & 50 & 50 \\ % & 10 & 10 \\
+ bandwidth (Mbit/s)
+ & 50 & 50 & 50 & 50 & 50 \\ % & 10 & 10 \\
\hline
latency (ms)
- & 0.02 & 0.02 & 0.02 & 0.02 \\ % & 0.03 & 0.01 \\
+ & 0.02 & 0.02 & 0.02 & 0.02 & 0.02 \\ % & 0.03 & 0.01 \\
\hline
Power (GFlops)
- & 1.5 & 1.5 & 1.5 & 1.5 \\ % & 1 & 1.5 \\
+ & 1.5 & 1.5 & 1.5 & 1.5 & 1.5 \\ % & 1 & 1.5 \\
\hline
size
- & 120 & 130 & 140 & 150 \\ % & 171 & 171 \\
+ & 110 & 120 & 130 & 140 & 150 \\ % & 171 & 171 \\
\hline
Precision
- & \np{E-11} & \np{E-11} & \np{E-11} & \np{E-11} \\ % & \np{E-5} & \np{E-5} \\
+ & \np{E-11} & \np{E-11} & \np{E-11} & \np{E-11} & \np{E-11} \\ % & \np{E-5} & \np{E-5} \\
\hline
\hline
Relative gain
- & 2.51 & 2.58 & 2.55 & 2.54 \\ % & 1.59 & 1.29 \\
+ & 2.53 & 2.51 & 2.58 & 2.55 & 2.54 \\ % & 1.59 & 1.29 \\
\hline
\end{mytable}
\end{table}
- Processor unit power : 1.5 GFlops;
- - Intracluster network : bandwidth = 1,25 Gbits/s and latency = 5E-05 ms;
+ - Intracluster network : bandwidth = 1,25 Gbits/s and latency = \np{E-5} ms;
- - Intercluster network : bandwidth = 5 Mbits/s and latency = 5E-03 ms;
+ - Intercluster network : bandwidth = 5 Mbits/s and latency = 5.\np{E-3} ms;
\end{itemize}
